This study has the general aim of determining the effect of long-term hypoxemia on carotid body sensitivity and interaction with central chemoreception and on its neurotransmitter metabolism. To these ends we will: (1) develop a preparation for neurophysiologic study of the intact carotid body; (2) determine the effects of long-term hypoxia on neurotransmitter metabolism of carotid body and CNS regions, and to determine the functional correlation of these metabolic changes with ventilatory adaptation; and (3) quantitate the interaction of peripheral and central chemoreception by combining techniques of ventricular-cisternal perfusion with recording from the intact carotid body preparation. Specifically, the effect of changing brain ECF pH on CNS afferent and efferent activity will be quantitated.